I. Field of the Invention
The invention is directed to a transducer apparatus and more particularly to means for focusing and collimating ultrasonic waves.
II. Description of the Prior Art
Testing systems employing ultrasonic waves are well known. These systems are generally of two types: contact testing systems in which a transducer for generating ultrasonic waves contacts a workpiece and the waves are transmitted through a liquid couplant layer, and immersion testing systems in which the transducer is spaced apart from the workpiece and the waves are transmitted into the workpiece through an intervening liquid in which the workpiece and transducer are immersed. Although it is possible with immersion testing to produce a narrow, focused, collimated beam of ultrasonic waves, efforts to realize such a result with contact testing generally have been unsuccessful.
Mere focusing of a rather large beam is possible with contact testing. Prior art devices generally employ a tube containing a column of water or other suitable fluid coupled to the transducer. An appropriate focusing device, such as a lens is disposed intermediate the transducer and the tube containing the water. The tube may be either sealed with a thin membrane at the end nearest a workpiece or the end nearest the workpiece may be open and a continuous flow of water may be discharged against the workpiece. There are many disadvantages with this type of testing. The amount of focusing obtainable is quite limited and in the second alternative mentioned above, the workpiece and surrounding area are exposed to a flow of water. Additionally, the lowest f number achievable is about 1.4. A further serious drawback is that this type of contact testing cannot produce a collimated beam of ultrasonic waves, which collimated beam of ultrasonic waves may be desirable for some test purposes.
To achieve high energy output and good sensitivity, prior art contact testing devices have relied on large transducers. However, the contact area of such transducers is very large. Further, the large beam produced by such large transducers makes testing more difficult, since the reflective area of a discontinuity is only a small percentage of the area of the cross-section of the beam.
In view of the above-mentioned problems, it is an object of the invention to provide an apparatus wherein a narrow, focused, collimated beam of ultrasonic waves is produced.
It is a further object of the invention to provide a focused and collimated beam of ultrasonic waves without using a coupling medium as the beam-forming vehicle.
It is another object of the invention to provide a contact testing apparatus wherein a focused and collimated beam of ultrasonic waves is produced and in which the beam forming vehicle need not contact the workpiece or the area surrounding the workpiece.
It is a still further object of the invention to provide a portable contact testing device.